One of the best-known methods of determining dielectric permeability of the material is to irradiate a sample with an electromagnetic wave using a double-arm emitter. This allows determining the dielectric permeability my measuring the changing difference between the signal's phases in “arms” of the emitter and the measuring length of the passed-through, angled wave. By changing the difference between the signal's phases in “arms” of the emitter, the dependence of the amplitude of the passed-through wave on the length of the “arm” is eliminated. Dielectric permeability can then be derived from the following formula:
      ɛ    =                            λ          0          2                                      Sin            2                    ⁢          Q                    ·                        (                                    1              Δ                        -                          1                              λ                b                                              )                2              ,where λ0 is free-space wavelength; λb is length of the wave in double-armed emitter; and Δ is period of amplitude “zero” the passed-through wave. Angle θ is chosen according to the ratio
            (                                    d            k                                λ            b                          -        1            )        <                            d          k                          λ          0                    ⁢              ɛSinθ              <          (                                    d            k                                λ            b                          +        1            )        ,where dk is maximum size of the emitter's “arm”, see, for example, USSR Patent No. SU 1800333 A1.
The primary disadvantage of this method is the fact that a contact is required between the emitter and a sample to determine dielectric permeability. Moreover, the sample should have a flat surface to maintain proper contact with the emitter. Thus, this method cannot be used for remote determination of dielectric permeability of the object.
A second method used to determine dielectric permeability of a dielectric object is irradiating the object with coherent microwave radiation at N-frequencies. The microwave radiation is reflected from a background reflector. A border between the object's layers, a boundary between the dielectric object and air, or a physical body, on which the irradiated object is placed, may serve as the reflector. The signal reflected from the dielectric object is then registered. Then it is transferred to the time domain. Peak temporal components in the temporal spectrum are determined and measured. This data is used to calculate the dielectric permeability and the thickness of the layers. Probing and receiving is made into a sector of angles. Dielectric permeability and thickness of layers are then determined from the formulae:
                    ɛ        i            =                                                  ɛ              i                                ⁢          Sin          ⁢                                          ⁢                                    θ                              nad                ⁢                                                                  ⁢                1                                            (                i                )                                      ·            c            ·                          (                                                t                  i                                -                                                      2                    c                                    ⁢                                                            ∑                                              p                        =                        1                                                                    i                        -                        1                                                              ⁢                                                                                                                        ɛ                            p                                                                          ⁢                        Δ                        ⁢                                                                                                  ⁢                                                  l                          p                                                                                                                      1                          -                                                                                                                                                      ɛ                                  1                                                                /                                                                  ɛ                                  p                                                                                            ·                                                              Sin                                2                                                                                      ⁢                                                          θ                                                              nad                                ⁢                                                                                                                                  ⁢                                1                                                                                            (                                i                                )                                                                                                                                                                                                                    )                                                2          ·                      (                                          d                2                            -                                                ∑                                      p                    =                    1                                                        i                    -                    1                                                  ⁢                                  Δ                  ⁢                                                                          ⁢                                                            l                      p                                        ·                                                                                                                        ɛ                            1                                                    ⁢                          Sin                          ⁢                                                                                                          ⁢                                                      θ                                                          nad                              ⁢                                                                                                                          ⁢                              1                                                                                                      ⁢                                                                                                                                                                                                    ɛ                            p                                                    -                                                                                    ɛ                              1                                                        ⁢                                                          Sin                              2                                                        ⁢                                                          θ                                                              nad                                ⁢                                                                                                                                  ⁢                                1                                                                                            (                                i                                )                                                                                                                                                                                                                              )                                ;                      Δ        ⁢                                  ⁢                  l          i                    =                        (                                    t              i                        -                                          2                c                            ⁢                                                ∑                                      p                    =                    1                                                        i                    -                    1                                                  ⁢                                                                                                                              ɛ                                                      p                            ⁢                                                                                                                  ⁢                            1                                                                                              ·                      Δ                                        ⁢                                                                                  ⁢                                          l                      p                                                                                                  1                      -                                                                                                                                  ɛ                              1                                                        /                                                          ɛ                              p                                                                                ·                                                      Sin                            2                                                                          ⁢                                                  θ                                                      nad                            ⁢                                                                                                                  ⁢                            1                                                                                (                            i                            )                                                                                                                                                                            )                ·                              c            ·                                          1                -                                                                            ɛ                      1                                                              ɛ                      i                                                        ⁢                                      Sin                    2                                    ⁢                                      θ                                          nad                      ⁢                                                                                          ⁢                      1                                                              (                      i                      )                                                                                                                2            ⁢                                          ɛ                i                                                          ,  where i is the number of the layer; ∈i and ∈p are dielectric permeability of i and p layers; ∈1 is the dielectric permeability of the environment in which probing and receiving of signals is made; Δ1 is thickness of i-layer;
      Δ    ⁢                  ⁢    l    =                    h        1            +              h        2              2  where h1 and h2 are heights between the border of the first and second layers respectively and points from which probing is made and signal receiving points; θ(i)nad1 is angle of received signal reflected from the border between i and i+1 layer, c is speed of light; t1 is frequency of peak i-constituent of the time spectrum which corresponds with the reflection of the signal from the border between i and i+1 layers, and d is projection of the distance between the point of probing and signal receiving point, see Russian Patent No. RU 2039352.
The main disadvantage of this method, which is taken as a prototype of the proposed invention, is the requirement of parallel arrangement of the layers of the dielectric object. If the object has multiple layers, its sides should be parallel. Due to these requirements this method could be used solely for custom-made objects with required features. This method also requires determined incidence and angles of reflection of the microwave radiation towards the dielectric object.
The aforementioned deems it impossible to use this method for practice in determining dielectric permeability of the moving and hidden object with non-parallel sides or layers, particularly for covert determination of the presence of dielectric explosives hidden on a human body. Dielectric permeability for the most part of such explosives lies between 2.9-3.1.